For the manufacture of optical information carriers and the like, such as compact discs, VLPs, NODs, recordable discs, use is made of an injection mould with a mould cavity in which the mechanical information to be carried by the information carrier is to be found in negative form. The information component carrying the relevant information can for instance be embodied as a part of the mould, or as a so-called xe2x80x9cstamperxe2x80x9d. A stamper is a plate generally embodied in nickel, on the active surface of which the information is pre-arranged by per se known means. The relevant information will generally be of the digital type and consist of an alternation of either elevations or recesses and flat, unprocessed parts. The information is generally recorded on the information carrier in a spiral-shaped track.
After an information component has been used for manufacturing a determined number of information carriers the quality of the information carriers manufactured therewith deteriorates and the information component in question must be replaced. The information component must thus be replaced when the desired number of information carriers has been manufactured or when it has manufactured the maximum number of information carriers acceptable within a set quality standard.
The object of the invention is to furnish provisions enabling a very rapid change of information components such as stampers in order to thus make the time in which the injection moulding machine is not being used as short as possible.
With a view thereto the invention provides an auxiliary device intended to be added to an injection moulding device for manufacturing disc-like information carriers,
which injection moulding device comprises:
a mould having at least two mould parts displaceable relative to each other,
which in a first relative position bound a mould cavity, the form of which corresponds with the form of the information carriers for manufacture, into which mould cavity debouches a feed for heated plastic,
and which in a second relative position are located at a distance from each other such that the mould cavity is accessible;
holding means for holding an insert plate in a desired position, for example an insert plate for placing against an end wall of the mould cavity, on which plate is found the information to be recorded onto the information carrier, such that an insert plate remains in position relative to the mould cavity when a formed information carrier is removed;
which auxiliary device comprises:
a supply holder in which at least one insert plate can be received;
transporting means for transporting successive insert plates between the supply holder and the mould,
which transporting means comprise two heads which are each adapted to displace successive insert plates in axial direction to and from said end wall, all of which plates are provided with a central continuous hole, and which two heads each comprise centering means for placing an insert plate in correct position relative to the end wall by making use of a continuous hole in an insert plate;
control means connected or connectable to the injection moulding device,
which are adapted to release the transporting means only in the second relative position of the mould parts in order to transport an insert plate from or to the mould,
and which are adapted to control the holding means,
wherein the transporting means are controllable by the control means.
The use of two heads has the great advantage that for instance in one joint movement or with two related movements the one head can remove an insert plate already present in the mould and the already waiting second head can then place a new insert plate without it first being necessary for the first head to place the removed insert plate back into the supply holder. It will be apparent that this double head according to the invention can very considerably reduce the time required to change insert plates.
A very simple embodiment is that wherein the heads are supported by a collective carrier which is controllable by the control means.
The auxiliary device can for instance be embodied such that the carrier has a degree of freedom of translation.
In an alternative the auxiliary device has the special feature that the carrier has a degree of freedom of rotation.
This latter variant is preferably embodied such that the carrier is pivotable round a pivot axis, relative to which the heads are equidistant.
In order to prevent dust, which is undesirable in the manufacture of information carriers, the embodiment is recommended in which the supply holder comprises a closable supply holder.
A specific embodiment has the special feature that the supply holder comprises individually closable compartments, in each of which can be received an information component.
A variant which very effectively prevents the information components being subject to picking up dust is that in which the supply holder can be connected to a source of substantially dust-free gas, such as air under a certain overpressure. In this context xe2x80x9coverpressurexe2x80x9d is understood to mean a pressure relative to the ambient pressure such that there is no danger of air from outside being drawn into the supply holder in uncontrolled manner through cracks. A small overpressure relative to the ambient pressure is sufficient for this purpose.
A specific embodiment has the special feature that each compartment can be connected to a source of gas under pressure.
An embodiment which lends itself easily to automation has the special feature that the supply holder and the transporting means are relatively movable and positionable such that the transporting means can remove an information component from the supply holder or place it therein at a chosen location thereof.
In addition to the provisions discussed in the two previous paragraphs, an auxiliary device operating fully automatically is also provided with a central processing unit in which is pre-recorded data relating to the information component present at each location in the supply holder and relating to a desired sequence for control of the positioning of the supply holder in relation to the transporting means.
An alternative has the special feature that the central processing unit comprises memory means into which is read in each case which information component is arranged at a specific location in the supply holder.
As the case arises, it may be practical if a transfer station is also situated between the supply holder and the injection mould. In this respect attention is also drawn to the fact that the supply holder and the transporting means have only to be relatively movable. The supply holder can thus for instance be mobile, while the transporting means are movable substantially in the same plane, while alternatively the supply holder can occupy a fixed position which is accessible at any desired location due to the multiple mobility of the transporting means.
The information components can be stored and transported vertically, horizontally or in any other desired position. The supply holder can be movable in linear or rotating manner relative to the transporting means. Combinations are also possible. The information components can be held in position in the injection mould with all suitable means. These means are for instance underpressure, mechanical means and magnetic and electromagnetic means. Reference is also made in this respect to EP-B-0 177 991.
In order to obtain a very reliable centering while completely avoiding possible damage to the insert plates, the auxiliary device can be embodied such that the centering means comprise a for instance blunt pin tapering toward the outside.
In order to bring an insert plate as rapidly as possible to the same temperature as the relevant mould wall and to place it such that shifting relative to this end wall through dilatation or contraction is avoided, the auxiliary device can advantageously be embodied such that the heads comprise heating means.
In some conditions it may be favourable not to have the device operate fully automatically but to have the option of intervening in a cycle. An auxiliary device suitable for this purpose has the special feature that the control means are adapted to control the heads such that they are temporarily halted in their path between supply holder and mould for manual placing or removal of an insert plate.
Any suitable electric motor can be used to control the transporting means in combination with position sensors or the like, on the basis of which the central processing unit can determine where a head is situated at any moment. Very simple however is the embodiment in which the transporting means comprise a stepping motor. This embodiment avoids the use of the position sensors in a negative feedback loop.
As discussed above, use can advantageously be made of a flow of dust-free gas through the supply holder.
In this respect the auxiliary device preferably has the feature that the gas flow is substantially laminar. A turbulent flow can have the drawback of stirring up possibly present and deposited dust particles.
The auxiliary device is preferably embodied such that the gas flow is directed downward. Stirring-up of deposited dust can hereby also be prevented.
A specific preferred embodiment comprises ionization means for ionizing the gas. Such an embodiment eliminates static charge of dust particles in the through-fed gas flow, whereby less deposition onto the information-carrying insert plate can take place.
An embodiment with ionization means is that in which the ionization means comprise corona means. As is known, a corona source can comprise a number of sharply pointed electrodes which have a very high potential relative to another surface, for instance in the order of 5-50 kV. An active corona source is recognizable from its light-emitting character, which indicates excited condition of the atoms present in the gas.
Other ionization means can also be used, for instance tribo-means and radio-active means. Corona means have the advantage however of enabling very simple embodiment and of operating in very stable and reliable manner.
A specific embodiment has the special feature that the central processing unit is also adapted to adjust process parameter values relevant for the injection moulding process on the basis of certain, predetermined properties of an insert plate, corresponding for instance with the playing time of a CD to be manufactured therewith. This variant can be incorporated in an auxiliary device in which, as according to an already stated aspect of the invention, the central processing unit comprises memory means into which is read in each case which insert plate is arranged at a specific location in the supply holder.
In the above mentioned embodiment in which use is made of a centering pin tapering toward the outside, the auxiliary device according to the invention can advantageously have the special feature that each head bears a centering pin narrowing toward its free end which during positioning and/or removal of an insert plate extends in coaxial relation to the mould cavity and which can co-act in positioning manner with a central positioning hole which debouches on the mould wall against which an insert plate must be positioned,
wherein the centering pin is arranged spring-loaded to the outside relative to an auxiliary head which is axially movable by means of drive means for placing and removal of an insert plate. Such a structure ensures that positioning of the insert plate relative to the relevant end wall can take place with very high precision. As a consequence of the fact that the centering pin has a tapering form, a completely exact centering takes place in all conceivable conditions. It will be apparent that a condition for good operation is that the edge of the hole in the relevant mould wall can always co-act with the tapering portion of the centering pin.
A specific embodiment has the special feature that the auxiliary head comprises an annular support surface for carrying an insert plate, in addition to a positioning cylinder which is placed coaxially with the centering pin and which co-acts in positioning manner with the central hole in the insert plate.
Very simple and reliable in operation is the variant in which the drive means comprise a number of pneumatic cylinders or bellows which are connected to an on/off switchable vacuum source and which are connected between a main frame of a head and the auxiliary head such that when the vacuum source is switched on the auxiliary head is displaced outward relative to said main frame, wherein after the vacuum source has been switched off the auxiliary head is returned to an inward directed rest position by resetting spring means. The use of bellows in particular enables a very inexpensive but nevertheless extremely reliable embodiment.
In the most refined form, an automatic, pre-programmable changing of the information components can take place with the auxiliary device according to the invention without any intervention by personnel.